1. Field of the Invention
The present invention relates to a power switching apparatus which is preferable for switching a two-wheel drive state and a four-wheel drive state, in a vehicle.
2. Description of the Related Art
In power switching apparatuses for a vehicle, as described in Japanese Patent Application Laid-Open No. 2001-80385 (JP-A), there are structures having the following features. A differential transmits rotation of a drive shaft to a wheel pair. A first rotary member corresponds to an output member of the differential in a side of one wheel, and a second rotary member is arranged to be relatively rotatable to the first rotary member and which integrally rotates with one wheel. A third rotary member integrally rotates with a case of the differential rotating in correspondence to the rotation of the drive shaft. A dog clutch can be switched among a first position at which a connection between the first rotary member and the second rotary member is cancelled, a second position at which the first rotary member and the second rotary member are connected, and a third position at which the first rotary member, the second rotary member and the third member are connected.
In the prior art, a two-wheel drive state in which rear wheels are only driven may be established, during which time the dog clutch is at the first position. A differential free state (a four-wheel drive state capable of absorbing rotation difference between right and left front wheels during a vehicle turning operation) in which four wheels are driven is established when the dog clutch is at the second position. A differential lock state (a direct-connection four-wheel drive state capable of integrally rotating the right and left front wheels so as to improve a traveling characteristics) in which four wheels are driven may be established when the dog clutch is at the third position.
In the conventional power switching apparatus, the differential mechanism for switching the two-wheel drive state, the four-wheel drive differential free state and the four-wheel drive differential lock state involves installation of a bevel gear. Therefore, the structure becomes complex and large in size.
Further, since the switching operation is executed by using the dog clutch, it is necessary to align phases for engagement and disengagement of a sleeve and a spline which constitute the dog clutch.